Many systems experience characteristics having quasi-periodic properties. For example, equipment containing load-bearing parts (e.g., rotorcraft, jet engines, HVAC chillers, electric motors, etc.) are used in many applications. Designers usually use conservative assumptions regarding the loads that the parts will encounter in service. In actual use, however, the parts in the equipment may encounter loads that are greater than anticipated, causing the life of the part to require service or replacement earlier than planned or part failure. Similarly, the part may encounter loads that are smaller than anticipated, causing unnecessary service scheduling when the part is still in good condition.
When designing each part, designers tend to be conservative and over-design parts having properties (e.g., strength, mass, shape, etc.) needed to withstand worst-case expected load levels. More particularly, individual parts may be designed assuming a maximum load level associated with each type of operating state and assuming a certain percentage of time spent in each state. The parts are then designed based on the anticipated maximum loads encountered during each state and the number of instances that each state is anticipated to occur. These estimates are usually conservative to ensure optimal operation for an extended time period, even under conditions that are more severe than normal.
The parts are also designed to withstand a maximum worst-case composite usage profile that reflects conditions that are harsher than normal. For example, the parts may be designed to withstand forces encountered by the most severely-used equipment. If the actual equipment operation is similar to the assumptions used during design of the equipment parts, the parts should last for the expected lifespan. As a practical matter, however, some equipment may be used in conditions that are more severe than assumed. For example, a rotorcraft used in combat will contain parts that will require replacement earlier than the expected lifespan, while a rotorcraft used in less demanding conditions will not and may even last longer than the expected lifespan.
It is not always possible to design parts that are strong enough to last indefinitely under all operating conditions because they would be too large, expensive and heavy to be practical. Because equipment parts are often expensive to replace, it is desirable to monitor the load on the part to determine whether a given part actually requires replacement. For example, if a part is designed with an expected lifespan of 10,000 hours, a part that has been used for 10,000 hours in mild conditions would probably not require replacement until much later, while a part used in combat may require replacement at the 10,000 hour mark.
Because of these varying operational conditions, it would be desirable to monitor the actual loads on a part during equipment use for optimizing part design, part weight management, equipment management, and other applications. However, the location and operation of the parts may make mounting and monitoring load sensors difficult or cumbersome, particularly for rotating parts, which would require data transmission paths between a moving sensor and a fixed receiver. Adding load sensors to all of the parts to be monitored increases the complexity of the equipment and requires additional electronics, which increase weight and cost.
There is a desire for an efficient, reliable, affordable, and robust way to conduct load monitoring. There is also a desire for a system that generates load estimates that are accurate enough to use as a basis for part design and monitoring based on the load estimates.